Anonymous is not so anonymous anymore. The computer hackers, chat-room denizens and young people who make up the loosely affiliated Internet collective have drawn the attention of the FBI, the Department of Homeland Security and other federal investigators. What was once a small group of pranksters has become a potential national security threat, federal officials say. The FBI has carried out more than 75 raids and arrested 16 people this year in connection with illegal hacking claimed by Anonymous.Since June, Homeland Security has issued three “bulletins” warning cybersecurity professionals of hacking successes and future threats by Anonymous and related groups — including a call in Manhattan to physically occupy Wall Street on Sept. 17 to protest various U.S. government policies.San Francisco police arrested more than 40 protesters last month during a rowdy demonstration organized by Anonymous that disrupted the evening commute. The group called for the demonstration after the Bay Area Rapid Transit system blocked cellphone service in San Francisco stations to quell a planned protest over a police shooting on a subway platform.“Anonymous’ activities increased throughout 2011 with a number of high-profile attacks targeting both public- and private-sector entities,” one of the bulletins issued last month said.Some members of the group have called for shutting down Facebook in November over privacy issues, though other Anonymous followers are disavowing such an attack, underscoring just how loosely organized the group is and how problematic it is to police.

“Anonymous insist they have no centralized operational leadership, which has been a significant hurdle for government and law enforcement entities attempting to curb their actions,” an Aug. 1 Homeland Security bulletin noted. “With that being said, we assess with high confidence that Anonymous and associated groups will continue to exploit vulnerable publicly available Web servers, Web sites, computer networks and other digital information mediums for the foreseeable future.”Followers posting to Twitter and conversing on Internet Relay Chat insist there are no defined leaders of Anonymous and that it’s more of a philosophy than a formal club, though a small group of members do the most organizing online.“Anonymous is not a group, it does not have leaders, people can do ANYTHING under the flag of their country,” wrote one of the more vocal members who asked not to be identified.

“Anything can be a threat to National Security, really,” the member said in an e-mail interview. “Any hacker group can be.”